This invention relates to the field of computers and computer systems. More particularly, the present invention relates to a method and apparatus for automatically detecting signal levels for buffer configuration.
In recent years, the price of personal computers (PCs) has rapidly declined. As a result, more and more consumers have been able to take advantage of newer and faster machines. Users in both the business and home markets are now purchasing computers for a variety of uses. Numerous peripheral devices, expansion boards, and add-on cards are also available for system upgrades. One common performance upgrade that consumers, especially in the graphic design and game arena, take advantage of is the graphics card.
As the technology in computer systems improves, there has been a move towards lowering the power consumption of computer systems. One attempt to reduce power consumption entails controlling the clock frequency at which a microprocessor operates and the power dissipation of the microprocessor. Another power saving method is to use software in controlling system power and shutting down system devices that are not needed. One power reduction method involves the use of low power circuit devices or lower voltage components in computers.
Low voltage components allow a computer system to operate with less power with no performance loss. Hence newly designed plug-in and expansion boards generally require lower voltages. However, PCs have been around for several years now. An extremely large amount of hardware including peripheral devices and plug-in cards are still in existence and available in the marketplace. Older generations of hardware technology are often referred to as legacy hardware. Legacy hardware may have special needs such as different board interconnects, memory requirements, and power supply voltages.
In order to build computers using the latest hardware devices and yet still maintain backward compatibility with legacy hardware, designer engineers are developing methods and apparatus to provide support in each system for multiple types of technology. For instance, some graphics cards use different signaling levels. One graphics card may allow signaling at the 3.3 volts level. Another graphics card may provide for 1.5 volts level signaling. Systems designed for only one signaling level would not be able to use cards that support other signaling levels.
Adding to the confusion are signaling methods that allow for multiple signaling levels. One such method is the Accelerated Graphics Port (AGP), where signaling can be done at either 1.5 volts or 3.3 volts. The higher 3.3 volts level allows commodity processes and legacy buffer designs to be used in enabling this signaling standard. The lower 1.5 volts level allows higher data transfer rates, lower power consumption at lower transfer rates for mobile systems, or more complex graphics systems with higher transistor count at the same power level. By going to lower voltages, a designer can add more gates and more features to the chip without adding more power. Power is cost on an add-in card. Power also adds cost for on-board regulators Too much chip power on the graphics controller may necessitate a xe2x80x9cfan-sinkxe2x80x9d, which is expensive in terms of the bill-of-materials cost. Systems having AGP devices that bridge the different signaling levels need to operate at both levels. Hence, computer designers need a means to control the interface of AGP devices according to the signaling level required.
Present designs in systems with AGP use an input pin to indicate the signaling level. In AGP, the AGP connector has a xe2x80x9ctype detectxe2x80x9d pin for programming the input/output (I/O) power supply. However, the value on the pin is not required to be at any particular logic level. Hence, in some instances, the pin may be floating at an intermediate potential anywhere between ground and a logic high state. Furthermore, the type detect pin has to be ignored for a certain amount of time during the power-up sequence so that an evaluation can be made at the correct time. The existing scheme requires the use of a dedicated pin for setting the buffer level. This requirement may be another disadvantage in some systems. The industry has continuously worked to decrease both the cost and footprint of computer systems as the size of components and circuit devices shrink. The capability of saving a pin on a component such as a memory controller hub (MCH) may help to reduce costs and design headaches.
A method for automatically detecting signal levels for buffer configuration is described. The method in one embodiment of the present invention first samples a first signal. The first signal is compared with a second signal to determine whether the first signal has a higher voltage potential than the second signal. The result of the comparison is latched. The result of the comparison is used to program buffer characteristics.